Vibration pickup comprising a pressure sleeve

ABSTRACT

A vibration meter having a pressure sleeve is proposed, in which the pressure sleeve ( 2, 22 ) may be mounted under pressure at a bottom surface ( 20 ) on a component causing vibrations, and the bottom surface ( 20 ) has a contour, prior to mounting, which runs radially inward in a concave manner. Furthermore, prior to mounting, the bearing surface ( 21 ) has a contour, which runs radially inward in a concave manner, the contour being dimensioned such that, after the mounting, at least one sensor arrangement ( 7, 5, 6, 8 ) lies substantially flat on the bearing surface ( 21 ) on the inside of the pressure sleeve ( 22 ).

BACKGROUND INFORMATION

[0001] The present relation is directed to a vibration meter having a pressure sleeve according to the species defined in the main claim.

[0002] German Patent 44 03 660 A1 already describes a vibration meter having a pressure sleeve which is used as a knock sensor for monitoring the function of an internal combustion engine in a motor vehicle. This pressure sleeve is fixedly mounted via a bearing surface on the component causing the vibrations, in this case to the engine block of the internal combustion engine.

[0003] With this known arrangement, the vibrations to be detected are knocking sounds of the internal combustion engine during operation, the sounds being transmitted via the pressure sleeve to a piezoceramic disk as the actual sensor element, which has interposed contact disks and insulating disks allowing the signal pick-up, and in this manner generates an analyzable output signal.

[0004] The manner of mounting or clamping of this sensor arrangement on the pressure sleeve and the mounting of the vibration meter on the vibrating component has a considerable influence in this case not only on the method of manufacture but also on potential faulty measurements and interferences in operation. In the case of this known vibration meter, the clamping of the sensor element having a plurality of component parts, such as a spring and a seismic mass, is accomplished with a ring nut, for instance, which is capable of being screwed onto a corresponding threat on the pressure sleeve.

[0005] When mounting the known vibration meter with the aid of an axially acting screw on the component causing the vibrations, the base surface of the pressure sleeve, which is concave from the outside toward the center bore, is pressed onto the surface of the component lying across from it. As a result of this pressure, the bearing surface of the pressure sleeve lying opposite inside, which supports the sensor element, also assumes the same angle at which the bottom surface runs concavely. Thus, a cavity may form between the bearing surface and the sensor arrangement, and here, in particular, the ceramic disk with the insulation and contact disks, in the region lying radially on the inside.

[0006] Since compensation for this cavity by elastic deformation of the relatively rigid sensor components is generally minimal, an optimal introduction of the vibrations to the actual sensor arrangement via the pressure sleeve is made more difficult.

SUMMARY OF THE INVENTION

[0007] The vibration meter having a pressure sleeve as mentioned at the outset, in which the pressure sleeve is mountable under pressure on a component causing vibrations using an initially concave bottom surface is advantageously refined according to the present invention in that the bearing surface for a sensor arrangement, which is supported on a bearing surface of the pressure sleeve situated inside of and opposite to the bottom surface, prior to mounting, has a contour, which runs radially inward in a convex manner. The contour of the bearing surface is dimensioned such that the sensor arrangement lies essentially flat on the bearing surface after mounting.

[0008] The bottom surface, which has the concave contour prior to mounting, is changed by the pressure of the mounting, usually via a screw guided through the center bore. In a particularly preferred specific embodiment, the angles at which the bottom surfaces are concave and the bearing surface is convex, are approximately identical prior to mounting, in the range of 10° to 20°, for instance, so that they always run in a parallel manner.

[0009] In this way, a flat resting surface for the sensor arrangement may also be produced in a particularly advantageous manner after the vibration meter is mounted, due to the described treatment of the bearing surface and the bottom surface. In this case, the essential components of the sensor arrangement for a knock sensor to be used as a vibration meter are a piezoceramic for generating an electrical signal and a superposed seismic mass, whose surfaces thus are always lying on top of one another in a plan-parallel manner.

[0010] These and other features of preferred embodiments of the present invention are derived not only from the claims but also from the specification and the drawings, it being possible to realize the individual features by themselves or together in the form of subcombinations in the specific embodiment of the present invention and in other fields, and these constituting advantageous and patentable embodiments for which protection is claimed here.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] An exemplary embodiment of the vibration meter having a pressure sleeve in accordance with the present invention are discussed with the aid of the drawings. The figures show:

[0012]FIG. 1 a section through a knock-sensor housing as vibration meter with a pressure sleeve according to the related art; and

[0013]FIG. 2 a detailed representation of a pressure sleeve according to the present invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0014]FIG. 1 shows a knock sensor as a vibration meter for an internal combustion engine, having an outer plastic housing 1 in which a pressure sleeve 2 is disposed. In its lower end region, pressure sleeve 2 has a flange-type collar 3 by which it rests with its lower bottom surface 20 on the engine block (not shown) whose vibrations are to be detected.

[0015] At outer circumference 4 of pressure sleeve 2, beginning at a lower bearing surface 21 at flange-type collar 3, the following components are disposed: An insulating disk 5, a first contact disk 6, a piezoceramic disk 7 as the actual sensor element, and above it, another second contact disk 6 as well as a second insulating disk 5. A seismic mass 8, which is pressed in the direction of piezoceramic disk 7 by an annular spring 9, is placed on top of this arrangement. Spring 9 is prestressed by a ring nut 10, which is screwed onto an outer thread 11 at the upper part of pressure sleeve 2.

[0016] In an integrated connector 12 of housing 1, which is especially produced by a plastic-injection molding process, electrical terminals 13 for contact disks 6 and plugs 14 are injection-molded. Plugs 14 are thus connected to the two contact disks 6, by which an electrical connection to the two sides of piezoceramic disk 7 is produced via the two contact disks 6, and it is possible to pick off the electrical voltage generated in response to a pressure load of piezoceramic disk 7 in the axial direction.

[0017] A (not depicted) mounting screw is also guidable through a central opening, or a bore 15, in pressure sleeve 2, by way of which this knock sensor may be mounted, indirectly or directly, as an entity on the engine block of the internal combustion engine. When the knock sensor is mounted, the entire torque exerted by the afore-mentioned mounting screw is transferred to pressure sleeve 2 via lower surface 20, that is, no force is exerted by the mounting on piezoceramic disk 7 as the sensor element.

[0018] A prestressing force is exerted in this case, due to the pressure by spring 9. The prestressing force is selected such that axial forces come to bear at piezoceramic disk 7 which are only just tolerable without lasting deterioration of the electrical signal; and these are also largely independent of thermal expansions and unavoidable compression of pressure sleeve 2 during mounting. The impulses exerted by seismic mass 8 in proportion to the vibrations of the internal combustion engine are converted to charge impulses in piezoceramic disk 7, which are analyzable in an appropriate device.

[0019] In the example known from the related art as shown in FIG. 1, bottom surface 20 has a conical shape sloping towards bore 15, so that an elevation is produced in the outer region of flange-type collar 3. Due to the conical shape of bottom surface 20, pressure sleeve 2 is now able to be pressed fully against the bearing surface of the engine block.

[0020]FIG. 2 shows a detailed representation of a pressure sleeve 22 according to the present invention, in which not only a conical contour of bottom surface 20, but also a correspondingly convex shape of bearing surface 21 is provided, in a revision of pressure sleeve 2 according to FIG. 1. To optimize the mounting of the entire vibration meter, angle α of the conical contour of bottom surface 20 and angle β of the convex contour of bearing surface 21 are relatively small, 10° to 20°, for example, steel or brass being used as the material for pressure sleeve 22. Preferably, both angles α and β are of equal size, so that after mounting piezoceramic 7, in particular, and seismic mass 8 are always superposed on one another in a plane-parallel manner.

[0021] When selecting angles α and β, it is also important that the conical region of bottom surface 20 comes to lie on the component from the outer edge when the (not depicted) mounting screw is tightened, that is, that first the contact area with the larger diameter and then, as the torque of the mounting screw increases, the other areas of the conical area are making contact with the component. In this manner, almost the entire conical area makes contact. The deformation, to which angles α and β need to be adjusted, preferably is to be entirely or predominantly in the elastic range of the material used for pressure sleeve 22, so that the conical shape may reform nearly completely once the mounting screw is loosened, due to so-called residual elasticity. 

What is claimed is:
 1. A vibration meter having a pressure sleeve, in which, using a base surface (20), the pressure sleeve (2, 22) may be mounted under pressure on a component causing vibrations, the bottom surface (20) having a contour, which runs radially inward in a concave manner prior to mounting and may be changed by the pressure in mounting, and having a sensor arrangement (7, 5, 6) and additional components (8, 9), the sensor arrangement supported at the outside of the pressure sleeve (2, 22) under an initial axial stress, on a bearing surface (21) of the pressure sleeve (2, 22) situated inside of and opposite to the bottom surface (20), wherein the contact area (21) has a contour, which runs radially inward in a convex manner prior to mounting and is dimensioned such that, after the mounting, at least the sensor arrangement (7, 5, 6, 8) lies essentially flat on the bearing area (21). 2) The vibration meter as recited in claim 1, wherein, the angles (α, β) at which the bottom surface (20) runs concavely and the bearing surface (21) runs convexly, are identical prior to mounting. 3) The vibration meter as recited in claim 2, wherein, the parallel angles (α, β) are in the range of 10° to 20°. 